System and method for demodulating global positioning system signals
First Claim
1. A global positioning satellite (GPS) demodulator configured to receive a GPS signal which includes modulated C/A code, L1 P-code, L2 P-code and encrypting W-code signals, the demodulator comprising:
- an L1 P-code generator configured to generate first and second L1 P-code signals that are local replica signals of the L1 P-code of the GPS signal;
a first demodulator configured to demodulate the GPS signal based on, in part, the first and second L1 P-code signals, to thereby generate first and second demodulated L1 P-code signals;
a first pair of integrate-and-dump (I&
D) filters configured to generate a first integrated L1 P-code signal by integrating the first demodulated L1 P-code signal and configured to generate a second integrated L1 P-code signal by integrating the second demodulated L1 P-code signal during a predetermined integration period;
a first thresholding module configured to generate a first switch control signal by comparing the first integrated L1 P-code signal to a first predetermined threshold value to determine whether the encrypting W-code changed polarity during the predetermined integration period; and
a first switch configured to output a first adjusting signal based on a signal derived from the first and second integrated L1 P-code signals and based on the first switch control signal, wherein the L1 P-code generator is further configured to be adjusted based on a signal derived from the first adjusting signal, to thereby accurately generate the first L1 P-code signal which tracks the L1 P-code of the GPS signal.
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Accused Products
Abstract
A GPS receiver uses the energy of the L1 and L2 GPS satellite signals to track the phase of the L1 and L2 P-code and the carrier phase of the L2 signal. The in-phase channel of the L1 signal, after L1 carrier demodulation with the aid of the publicly known C/A code, is first correlated with the P-code from a P-code generator in the L1 channel of the receiver. The correlation output is filtered over two W-bit periods, using an integrate-and-dump (I&D) filter, to determine whether a polarity change has occurred. Similarly the in-phase and quadrature channels of the received L2 Y-code signal are correlated with the P-code from the P-code generator in the receiver L2 channel and I&D filtered over the corresponding period of two W-bits. Polarity transitions between the two W-bits over the I&D integration period are detected by a threshold comparison with the I&D output of the L1 punctual P-code correlation signal. If a polarity change has occurred, the L1 and L2 I&D outputs are not used for L2 carrier demodulation. When there is no polarity change, the I&D output of the L1 in-phase Punctual P-code correlation is combined with the L2 in-phase Punctual P-code correlation in accordance with the L1 and L2 signal power ratio. This summed signal is multiplied with the I&D output of the L2 quadrature channel early-late P-code correlation to obtain a product signal that provides an estimate of the L2 carrier phase.
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Citations
28 Claims
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1. A global positioning satellite (GPS) demodulator configured to receive a GPS signal which includes modulated C/A code, L1 P-code, L2 P-code and encrypting W-code signals, the demodulator comprising:
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an L1 P-code generator configured to generate first and second L1 P-code signals that are local replica signals of the L1 P-code of the GPS signal; a first demodulator configured to demodulate the GPS signal based on, in part, the first and second L1 P-code signals, to thereby generate first and second demodulated L1 P-code signals; a first pair of integrate-and-dump (I&
D) filters configured to generate a first integrated L1 P-code signal by integrating the first demodulated L1 P-code signal and configured to generate a second integrated L1 P-code signal by integrating the second demodulated L1 P-code signal during a predetermined integration period;a first thresholding module configured to generate a first switch control signal by comparing the first integrated L1 P-code signal to a first predetermined threshold value to determine whether the encrypting W-code changed polarity during the predetermined integration period; and a first switch configured to output a first adjusting signal based on a signal derived from the first and second integrated L1 P-code signals and based on the first switch control signal, wherein the L1 P-code generator is further configured to be adjusted based on a signal derived from the first adjusting signal, to thereby accurately generate the first L1 P-code signal which tracks the L1 P-code of the GPS signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of processing a global positioning system (GPS) signal which includes modulated C/A code, L1 P-code, L2 P-code and encrypting W-code signals, comprising the steps of:
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demodulating the GPS signal based on, in part, first and second L1 P-code signals that are locally generated replica signals of the L1 P-code of the GPS signal, to thereby generate first and second demodulated L1 P-code signals; separately integrating the first and second demodulated L1 P-code signals over a predetermined integration period, to thereby generate first and second integrated L1 P-code signals; comparing the first integrated L1 P-code signal to a first predetermined threshold value to determine whether the encrypting W-code has changed its polarity during the predetermined integration period; and adjusting the first L1 P-code signal based on the first and second integrated L1 signals and based on whether the encrypting W-code changed polarity during the integration period, to thereby accurately generate the first L1 P-code signal which tracks the L1 P-code of the GPS signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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Specification